<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>DOM 对象转成 jQuery 对象</title>
  <script type="text/javascript" src="./script/jquery-3.6.0.min.js"></script>
  <script type="text/javascript">
      window.onload=function () {
        var username = document.getElementById("username");
        alert("username="+username.value)
        var $username = $(username);
        alert("username value="+$username.val())

      }
  </script>
</head>
<body>
用户名 <input type="text" id="username" name="username" value="韩顺平教育"/>
</body>
</html>